This competing continuation application for an ADAMHA Research Scientist Development Award (Level II) proposes studies of the ontogeny of ingestion and its behavioral, physiological, and neural organization. The proposed experiments exploit a developmental system of independent ingestive behavior (devised and described by my lab) and techniques for systems-level, neural analysis recently developed for infant rodents. The control of individual components in the ingestive sequence will be studied in young rats. Emphasis will be placed on the oral response component and in particular on the decrement in oral responsiveness that occurs during feeding experience. This intrinsic, habituation-like mechanism may be a principal integrator of ingestion-related signals. An integrative function for oral habituation would be indicated by influences of physiological state and postingestive signals on habituation parameters such as the initial level of responsiveness, rate of decrement, or duration of decremented responsiveness. The relation of the oral component to earlier components in the sequence will be assessed in experiments measuring olfactory orienting, and the brainstem representation of the oral habituation process will be evaluated in decerebrate pups. The proposed experiments offer a unique conceptualization of ingestion that may contribute to a new, more complete, understanding of feeding control. These experiments will extend our ontogenetic analysis of an appetitive system, one that can be followed from birth and manipulated in a controlled fashion, and in which maturing neural systems can be related to changes in behavioral organization.